This invention relates to a device for distributing motive power between the front and rear wheels of a four wheel drive vehicle.
An example of an existing type of device for such distribution of motive power is shown in FIG. 1. That is to say, the hollow shaft 101, which receives input from the engine which is the device for driving the vehicle (the engine is outside of this figure), is supported inside the transfer case 103 in such a way that it is free to rotate, and is solidly coupled to the differential case 107 of the differential device 105 on its output side. The pinion shaft 109 is fixed to the differential case 107; the pinion gear 111 inside the differential case 107 is supported by the pinion shaft 109 in such a way that it is free to turn. The pinion gear 111 is meshed with a pair of side gears 113 which are opposite each other with respect to the center of the above-mentioned hollow shaft 101. One of the side gears 113 is coupled to one end of the front wheel drive shaft 115; the front wheel drive shaft 115 passes through the center of the above-mentioned hollow shaft 101 and extends to the front wheels which are off of the figure. The other side gear 113 is coupled to one end of the intermediate shaft 117 which is concentric with the above-mentioned hollow shaft 101. The other end of the intermediate shaft 117 is supported by the transfer case 103 through the bearing 119. The intermediate gear 121 is fixed to the intermediate shaft 117, and in turn the intermediate gear 121 is meshed with the input gear 125 of the rear wheel drive shaft 123. The rear wheel drive shaft 123 is located above the intermediate shaft 117 and is supported by the transfer case 103 in such a manner that it is free to rotate, and extends to the rear wheels which are off the figure. Meanwhile, the first lock member 129, which has the splines 127 on its outer circumference, is fixed to the above-mentioned intermediate shaft 117, while the second lock member 133, which has splines 131 of the same diameter as the splines 127, is fixed to the above-mentioned differential case 107. The splines 127 are meshed with the sleeve 135; by means of sliding motion, it is possible for both the splines 127 and the splines 131 to be meshed at the same time.
Input which is received from the engine is distributed by the differential case 107, the pinion shaft 109, the pinion gear 111 and the side gears 113, causing both the front wheel drive shaft 115, and the intermediate shaft 117, intermediate gear 121, input gear 125 and rear wheel drive shaft 123, to rotate. These drive shafts in turn transmit power to the front wheels and the rear wheels, which are off the figure.
When a difference arises between the rotation rates of the front wheel drive shaft 115 and the rear wheel drive shaft 123, the differential device 105 acts to maintain smooth transmission of power. When a differential lock is necessary, the sleeve 135 is caused to slide by the operation of a differential lock lever, which is off the figure next to the driver's seat, so that both splines 127 and 131 are meshed at the same time, causing the first lock member 129 and the second lock member 133 to be joined together as one body. In addition, since the rear wheel drive shaft 123 is located above the hollow shaft 101 and the intermediate shaft 117 which is concentric with it, it is easy to maintain the height above ground of the rear wheel drive shaft 123 which extends a long distance to the rear of the vehicle. This feature is particularly advantageous in off-road operation.
However, in this type of conventional power distribution device, the intermediate shaft 117 which has the intermediate gear 121 must be provided, and the transfer case 103, which extends along the length of the vehicle from front to rear, becomes extremely long. This in turn means that in order to provide a power distribution device, severe restrictions must be placed on the design of the other parts, and one consequence of this is an increase of the overall weight. In addition, the number of parts is increased by the addition of the intermediate shaft 117 and the bearing 119 which connects it to the transfer case 103, which makes assembly and supervision of parts more complicated.
In contrast to this type, there are also transmission systems in which the rear wheel drive shaft is not located above the intermediate shaft 117, but the intermediate shaft 117 itself is used as the rear wheel drive shaft. In this case the intermediate gear 121 becomes unnecessary and the total length of the system from front to rear of the vehicle is reduced by the length of the intermediate gear, and the number of parts is reduced. However, the height above ground of the rear wheel drive shaft, which extends a long distance to the rear of the vehicle, cannot be maintained, causing a reduction in performance off roads which tends to defeat the purpose of the four wheel drive vehicle.